Immunization is a critical intervention for achieving the Millennium Development Goal of reducing deaths among children less than five years of age (MDG4) by two-thirds. More than 100 million children are vaccinated each year, protecting them against life-threatening diseases (WHO and UNICEF, 2010). Immunization is considered to be one of the ‘best buys’ in public health (WHO and UNICEF, 2010; World Bank 2010). Traditional vaccines cost pennies per dose and provide health benefits not only for the immunized child, but also for the community in which a child lives through herd immunity. In addition, studies have shown that immunization extends life expectancy and the time spent on productive activity later in life, thereby contributing to economic growth. Given the public goods aspect of immunization and its potential returns for growth and poverty reduction, this is an intervention definitely worth investment by governments. While newer vaccines are more expensive on a per dose basis, they have been shown to be highly cost-effective investments. The purpose of this analysis is to summarize historical trends in immunization costs and financing, both for routine services and campaigns, as countries have introduced new vaccines. The main audience for this document is national, regional, and global technical staff working on national immunization programs.